Cloth pressers of sewing machines press, from above, by spring pressure, a sewing object placed on a sewing plate and thereby secure necessary contact pressure between the sewing object and feed teeth that emerge from below the sewing plate and sink to below it. With this structure, as the thickness of a sewing object increases, the cloth presser comes to crush the sewing object to possibly disable proper feeding of the sewing object.
A sewing machine for solving the above problem is known (refer to JP-A-2008-200311, for example). This sewing machine is equipped with a pulse motor as a drive source for elevating and lowering a pressing rod, a rack-formed member which is fitted with a top end portion of the pressing rod so as to be able to be elevated and lowered, a pinion gear which is in mesh with the rack-formed member and is rotated by the pulse motor, a stop ring which is fixed to the top end of the pressing rod, a pressing rod holder which is fixed to a middle portion, in the height direction, of the pressing rod, and a pressing spring through which the pressing rod is inserted between the rack-formed member and the pressing rod holder. The pressing rod is elevated or lowered by driving the pinion gear by the motor. A small presser lifting function is provided which enables proper feeding of a thick sewing object by performing a control of lifting up the cloth presser to a position (small presser lift height) that is somewhat above the needle plate.
However, in the above conventional sewing machine, the compression of the pressing spring which is disposed between the rack-formed member and the pressing rod holder is canceled when the rack-formed member is elevated by rotation of the pinion gear. Thus, the cloth presser exerts no pressing pressure on a sewing object when the small presser lifting function of having the presser lifted above the needle plate by 0 to 2.5 mm is performed.
The cloth presser exerting no pressing pressure on a sewing object raises, for example, a problem that where the sewing object is a stack of two cloths, the lower cloth is moved (fed) a much longer distance by the feed teeth than the upper cloth to produce a deviation between them.